Conventionally, various target object detection devices for transmitting radio waves to detect a target object based on the echo signals of the transmitted radio waves have been devised. In such target object detection devices, for example a target object detection device equipped in a ship, a threshold for a target object detection may be set for discriminating a target object, such as another ship or a land, from a sea clutter or a noise.
As a conventional method of setting a threshold, there is a method of calculating a moving average by using a group of echo signals aligned along a distance direction, that is a direction away from an antenna where the antenna is set as a reference position (so called CFAR) exists. Further, JP2008-256626A discloses a method of calculating a histogram of a group of echo signals aligned along a distance direction.
However, in the method of using the moving average, if a target object such as another ship or a land exists within a zone where the moving average is calculated, a threshold is increased corresponding to a level of an echo of the target object and the echo of the target object ends up being suppressed.
Further, in a case where the number of sample echoes of the target object within an area where a histogram is calculated is small and/or a level difference between a clutter and the target object echo is small, a trough to clearly distinguish the target object from the clutter does not appear within the histogram, and therefore, it is difficult to determine the threshold.